pth12040 Astec Powe, pth12040 Datasheet - Page 8

• Manufacturer Part Number: pth12040
• Description: Pth12040 12vin Single
• Manufacturer: Astec Powe

From the moment a valid input voltage is applied, the soft-start
control introduces a short time delay (typically 8ms to 15ms) before
allowing the output voltage to rise. The output then progressively
rises to the module’s setpoint voltage. Figure 7 shows the soft-start
power-up characteristic of the 18A output product (PTH12020W),
operating from a 12V input bus and configured for a 3.3V output. The
waveforms were measured with a 5A resistive load, with Auto-Track
disabled. The initial rise in input current when the input voltage first
starts to rise is the charge current drawn by the input capacitors.
Power-up is complete within 25ms.
HORIZ SCALE: 5 ms/Div
8 8
Figure 6 - Power-up Characteristic
File Name: an_pth12040.pdf Rev (02): 21 Dec 2005
lin (5A/Div)
Vin (5V/Div)
Vo (1V/Div)
7. Feature Set
7.1 Adjusting the Output Voltage
The Vo adjust control (pin 17) sets the output voltage of the
PTH12040 product. The adjustment range is from 0.8V to 5.5V. The
adjustment method requires the addition of a single external resistor,
Rset, that must be connected directly between the Vo Adjust and
GND pins
for a number of standard voltages, along with the actual output
voltage that this resistance value provides.
For other output voltages the value of the required resistor can either
be calculated using the following equation, or simply selected from
the range of values given in Tables 5. Figure 7 shows the placement
of the required resistor.
Table 4 - Preferred Values of R
V
out
Standard
5.0V
3.3V
2.5V
2.0V
1.8V
1.5V
1.2V
1.0V
0.8V
1
. Table 4 gives the preferred value for the external resistor
GND
1 3 5
PTH12040
PTH12040 Single Series | Application Note 193
Figure 7 - Adjust Resistor Placement
10 13 16
GND
R
set
-Sense
+Sense
V
(Preferred Value)
Equation 1
o
Adj
V
17
3.01kΩ
4.99kΩ
6.34kΩ
9.76kΩ
18.2kΩ
38.3kΩ
1.5kΩ
205Ω
Open
o
R
1%
0.05W
set
SET
12
15
14
11
9
for Standard Output Voltages
+
C
330µF
o
1
V
+
+Sense
out
-Sense
5.008V
3.303V
2.500V
1.997V
1.796V
1.498V
1.202V
1.000V
0.800V
C
330µF
GND
V
(Actual)
o
o
2